It is known to mount a piece of office equipment on an articulated-arm holder which allows the equipment to be moved about above the work surface while it is solidly supported so that it can be used. A telephone, adding machine, or keyboard, for instance, is frequently pulled over to the user when it is going to be used heavily, but is pushed back when subjected to lighter use.
A standard such device as described in German patent 2,819,976 has a stationary column that projects upward from the anchor surface and that can even pivot thereon about its upright longitudinal axis. An inner arm has an inner end pivoted about an inner horizontal axis on the upper end of this column and has an outer end. In turn an outer arm has an inner end pivoted at an outer horizontal axis on the inner-arm outer end and an outer end provided with some form of support on which the piece of equipment in question is held or rests. A nonextensible link has an inner end pivoted on the column offset from the inner pivot axis and an outer end pivoted on the inner end of the outer arm offset from the outer axis. This link extends parallel to a longitudinal axis of the inner arm, that is parallel to a plane through the two support axes so as to form with the inner arm a parallelogrammatic linkage.
As a result the equipment support plate always lies at the sam angle relative to the horizontal. This position is normally flat, that is with the equipment in its normal horizontal orientation. When, however, the equipment has been pushed back, with the inner and outer arms both generally vertical, this horizontal orientation makes the equipment difficult to use. For example, when an adding machine is pushed back toward the rear of the desk it is difficult to see its display without tipping it up.